YELLOW AND ALL-RED INTERVALS: HOW TO IMPROVE SAFETY AND REDUCE DELAY?

Abstract

Yellow and all-red intervals are intended as a margin of safety. The duration of change intervals needed for safe stopping or crossing of vehicles is not the same for all traffic conditions and patterns. Thus some traffic patterns may not need the full designed intervals’ durations as a safety margin; while at other times, they are not sufficient due mainly to drivers trying to avoid stopping at red lights. The challenge for traffic engineers is to minimize the intersection delay and at the same time maximize intersection safety. A methodology for providing variable length yellow and all-red intervals, based on traffic responsive sensors and logical commands, is outlined. The methodology stresses that safety is improved in some cases over the designed fixed yellow and all-red intervals, but never compromised lower than the default fixed yellow and all-red intervals. In addition, delay is reduced for various traffic patterns. Adhering to traffic agencies standards and regulations is addressed, not only to outline the practical limitations, but also to introduce discussion for potential positive changes.